5f - S ' J 



H d 



UNITED STATES DEPARTMENT OF AGRICULTURE 

BULLETIN No. 944 

Contribution from the Bureau of Animal Industry 
JOHN R. MORLER, Chief 





Washington, D. C. 



May 12, 1921 



THE ALCOHOL TEST AS A MEANS OF DETERMIN- 
ING QUALITY OF MILK FOR CONDENSERIES. 

By A. O. Dahlberg and H. S. Garner, Research Laboratories, Dairy Division. 



CONTENTS. 



Review of previous work 

Test methods used 

Experiments at Grove City creamery- 
Comparison of acidity and alcohol 

tests of milk for condensing 

Relative value of acidity and alco- 
hol tests 



Page. 
1 



Experiments at condenseries. 

Work at Factory A 

Work at Factory B 

Conclusions 

List of references 



Page. 

0 
9 
11 
13 
13 



REVIEW OF PREVIOUS WORK. 

The urgent necessity for some means of determining- the quality 
of milk received at condenseries and other dairy manufacturing 
plants has resulted in the continued use of the acid test even after 
its defects have become generally recognized. This test is based on 
the assumption that a titratable acidity above the normal for fresh 
milk indicates an increase in acidity due to bacterial action. 

It is well known, however, that a certain part of the alkali added 
to milk to obtain an end point with any given indicator is combined 
with constituents of the milk other than the acids. While this has 
been recognized it has not been generally realized how great a varia- 
tion in the apparent acidity may be due to this cause. It has been 
recently pointed out by Rice (l) 1 that the casein and the phosphates 
both combine with alkali and are subject to a sufficient variation to 
cause in some instances an apparent high acidity in fresh milk. 

Our own experience, which is not unusual, has shown that not 
infrequently milk rejected because of high acidity was fresh milk 
in which bacterial action was highly improbable. In making evapo- 
rated milk the most essential characteristic is the ability of the milk 

1 See list of references at end of bulletin. 

27179° — 21 



2 BULLETIN 944, U. S. DEPARTMENT OF AGRICULTURE. 

to withstand a temperature sufficiently high to insure the subsequent 
sterilization without causing an objectionable curd. While it is as- 
sumed, and no doubt correctly, that acidity is an important factor 
in determining the coagulating point of concentrated milk, it is by 
no means certain that other factors may not be of equal or even 
greater importance. Sommer and Hart (2) have shown that there 
is no consistent relation between the titratable acidity and the heat 
coagulating point of milk. This they found also to be true of the 
hydrogen-ion concentration or true acidity of the fresh milk, but 
they express the opinion that it may become a factor under com- 
mercial conditions. They found, on the other hand, that the varia- 
tions which occur normally in certain of the ash constituents have 
an important part in determining the temperature at which it 
coagulates. 

The titration of milk in the usual way will give no indication of 
the condition of the ash and may be very misleading as to the hydro- 
gen-ion concentration. 

The alcohol test has been used to a limited extent for determining 
the quality of milk with special reference to its sanitary condition. 

This test is usually made by mixing equal volumes of milk with 68 
to 75 per cent alcohol and observing whether a coagulation results. 
It is generally considered that a coagulation indicates bacterial 
change in the milk, but Auzinger (3) shows that fresh milk not in- 
frequently coagulates under these conditions and offers some evi- 
dence to show that it is due to changes in the milk salts, particularly 
in the calcium. Ayers and Johnson (4) show that while the alcohol 
test becomes positive when an appreciable amount of acid or rennet 
is produced in the milk there is no consistent relation between the 
alcohol test and the total number of bacteria present. 

They found that while the addition of acid phosphates to milk in- 
creased the tendency to coagulate with alcohol, the neutral or dibasic 
phosphate had the opposite effect. When dibasic phosphate is added 
to milk considerably more acid is required to produce a positive 
alcohol test than with the normal milk. 

While the work of Ayers and Johnson shows that the alcohol test 
is not a reliable index of the sanitary quality of the milk, there is a 
possibility that its action on milk may be correlated with the heat 
coagulation point of the evaporated milk in such a way as to render 
it of some value in grading milk in condenseries. 

TEST METHODS USED. 

The alcohol test as used in this investigation was made by mixing 
equal parts of 75 per cent alcohol and milk and observing whether 
coagulation takes place. In case the milk shows a visible coagulation 

— ~- -•• — ., » .~«. . 

LIBRARY OPf^CNGRtSS ! 

MAY 261921 

I DOCUMENTS UiVlSIOM 



DETERMINING QUALITY OF MILK FOR CONDENSERIES. 3 

it is considered unsafe from the standpoint that the milk after 
evaporation will not stand the heat necessary for sterilization with- 
out becoming curdy. The test is practical and easy to make at the 
weigh room. The test as used in this work was made by adding 
1 c. c. of milk to a small test tube containing 1 c. c. of alcohol and 
mixing at once by inverting once or twice while holding a finger 
over the top. Any reaction that takes place will be very quickly 
evident, the large majority of tests showing coagulation immediately 
or giving no reaction at all. The gradation of coagulation is shown 
by the size of the curd particles formed. Unless the curd particles 
formed are small the reaction is not at all difficult to distinguish, 
even by one not familiar with the test. A mixture of milk and 
alcohol giving 'a negative reaction immediately breaks clear from 
the walls of the test tube, while a mixture giving a coagulation 
of fine particles will leave the walls of the test tube cloudy. Mix- 
tures showing a medium or large particle curd formation are readily 
discernible because of the adherence of the curd particles to the 
walls of the test tube. 

In the work of grading the milk at a condensery on a commercial 
basis two small brass dippers of 2 c. c. capacity each were used. 
Thirty test tubes arranged in a block of wood 3 inches wide, 2 inches 
deep, and 18 inches long, having three rows of holes of the proper 
diameter and depth, were first filled with 2 c. c. of the 75 per cent 
alcohol by means of one of the brass dippers. Two men working 
together then went through the individual cans, taking 2 c. c. of milk 
from each and mixing it with the 2 c. c. of alcohol. No more time 
was required than is necessary in making the acidity test. 

The first work attempted with the alcohol test was to determine 
whether any correlation existed between the coagulation and the 
acid content of milk as measured by the usual titration method. 
Samples of milk were taken from individual patrons at the weigh 
room of the Grove City, Pa., creamery for the observations made. 
Reactions with 75 per cent ethyl alcohol and titratable acidity were 
determined shortly after taking samples and at stated intervals on 
those not showing positive coagulation with alcohol, until such action 
occurred. All samples which did not show coagulation with alcohol 
at the outset were held in a water bath at 35° to 37° C. (95° to 
98.6° F.) during subsequent observations. A tabulation of 211 
samples of milk handled according to the method outlined shows 
conclusively that there is no direct relation between the coagulation 
of the milk with 75 per cent alcohol and the acid content of milk 
as measured by the titration method. 



4 BULLETIN 944, U. S. DEPARTMENT OF AGRICULTURE. 



EXPERIMENTS AT GROVE CITY CREAMERY. 

COMPARISON OF ACIDITY AND ALCOHOL TESTS OF MILK FOR CONDENSING. 

Finding no consistent relation between the coagulation of milk 
by alcohol and its acidity content as shown by the titration method, 
work was started to ascertain the relative value of the two tests. 
Samples of milk, representing all conditions met with at the con- 
densery, were taken at the weigh room of the Grove City creamery. 
Five pounds of each sample selected — which in the large majority 
of cases represented a mixed milk of some particular patron's herd — 
was evaporated in a 10-liter flask under a vacuum of 25 to 27 inches 
to a concentration of 2^ to 1, the time required being from 50 to 70 
minutes, with a temperature of 40° to 50° C. (104° to 122° F.) . The 
evaporated milk was placed in baby-size tins and sterilized in an 
autoclave for 30-minute intervals at 121.1°, 112.8°, and 107.2° C. 
(250°, 235°, and 225° F.). Portions of evaporated milk in 100 c. c. 
Erlenmeyer flasks were run in the autoclave at the temperatures used 
and also at 100° C. (212° F.) for 30 minutes to note the extent of 
coagulation. When sterilization at 112.8° C. (235° F.) for 30 
minutes indicated that the product would not stand a higher process- 
ing, the next lower temperature was used, only two temperatures 
higher than 100° C. (212° F.) being used. The cooled cans of steri- 
lized milk were shaken for one minute before examination for gen- 
eral physical appearance and curdiness. 

The main observation of the sterilized samples of evaporated milk 
concerned the extent of coagulation and whether or not they showed 
curdiness after shaking. Curdiness of shaken samples was de- 
termined by the physical appearance of the product and by mixing 
a portion of it with hot water. In reporting on whether or not the 
sterilized samples were curdy after shaking, the temperature of 
112.8° C. (235° F.) for 30 minutes was used as a standard of compari- 
son. In the large majority of instances the curdiness was pronounced 
enough to leave no doubt as to the accuracy of decision, and the 
sample sterilized at the lower temperature quite generally substan- 
tiated the classification given on the basis of the standard tempera- 
ture used. On the other hand, the samples showing no curdiness 
after sterilization were in most cases not at all difficult to classify, as 
they showed, in general, less coagulation even with the higher 
temperature. 

Table 1 shows the results of sterilization pf 90 samples of milk of 
varying acidity, 45 of which coagulated with 75 per cent alcohol. 
Forty-three of the 45 when evaporated and sterilized at 112.8° C. 
(235° F.) for 30 minutes showed curdiness after shaking. Coagula- 
tion of practically all these samples when evaporated was very pro- 
nounced, in some instances being so hard that it was impossible in 



DETERMINING QUALITY OF MILK FOR CONDENSERIES. 5 



any manner to reduce the extreme lumpiness. Some of the samples 
of low acidity showed as objectionable a curdiness as those of the 
higher acidity, indicating the reliability of the alcohol test and un- 
reliability of the acid test in picking out those which will not stand 
the sterilization necessary in manufacturing evaporated milk. 

The table shows also the result of sterilization upon 45 samples of 
milk of varying acidity, all of which showed a negative reaction with 
75 per cent alcohol. Forty-two of the 45 when evaporated and 
sterilized showed no curdiness after shaking. 

Table 1. — Comparison of alcohol and acid tests at Grove City creamery. Milk 
concentrated 2\ to 1 and sterilized at 235° F. for SO minutes. Effect of sterili- 
zation noted after shaking for 1 minute. 





Coagulation with 75 per 
cent alcohol. 


No coagulation w ith 75 
per cent alcohol. 


Acidity. 


Total 


Effect of steri- 
lization. 


Total 


Effect of steri- 
lization. 




samples. 


Curdy. 


Not 
curdy. 


samples. 


Curdy. 


Not 
curdy. 


Per cent. 
0. 14 to 0. 15 
. 15 to . 16 
. 16 to . 17 
.17 to .18 
.18 to .19 
. 19 to . 20 
. 20 to . 21 


3 


3 


0 








5 

10 
11 

10 
5 
1 


5 
8 
11 
10 
5 
1 


0 
2 
0 
0 
0 
0 


1 

9 

12 
11 
10 

2 


0 
0 
1 
1 
0 
1 


1 

9 
11 
10 
10 

1 


Total. . . . 


45 


43 


2 


45 


3 


42 



It seems quite certain that there is some condition of raw milk 
coagulating with 75 per cent alcohol, making it impossible to sterilize 
without getting a curdy finished product, for such milks when evapo- 
rated and sterilized give a much firmer coagulation than those show- 
ing a negative reaction with 75 per cent alcohol. In some instances 
the coagulation, even at the lower temperatures used, is such that the 
product turns to a hard, cheesy mass incapable of improvement with 
long-extended shaking. Figure 1, showing the type of curd ob- 
tained in sterilization, indicates clearly the difference which must 
exist in the condition of milk coagulated with 75 per cent alcohol. 
Only 6.7 per cent of the samples made from milk coagulating with 
alcohol gave a soft curd, the remainder giving either a firm or a hard 
curd, both of which are as a rule difficult to shake out to give a 
product showing no curdiness. With the evaporated samples from 
raw milk not coagulating with 75 per cent alcohol 88.9 per cent gave 
either a soft curd or no coagulation at all, the remaining 11.1 per 
cent giving a firm curd. The soft curds shake out very easily, giv- 
ing a smooth-bodied product of good consistency showing no curdi- 
ness. 



6 



BULLETIN 944, U. S. DEPARTMENT OE AGRICULTURE. 



The difference in the effect of sterilization upon evaporated milk 
made from raw milk, showing negative or positive reaction with 
75 per cent alcohol is further emphasized in figure 2, which shows 
the curdiness found at all temperatures used. 

To get complete figures on all the four temperatures it was as- 
sumed in compiling these data that a sample showing curdiness at a 
temperature actually used would show curdiness at any higher tem- 
perature. With raw milks showing negative reaction with 75 per 

Raw milk curd Una Raw milk not curd Una 
with 157 0 a/cohol with 157c alcohol 




Fig. 1. — Types of curd obtained in sterilization of 
evaporated milk. 



cent alcohol only 4.4 per cent of the evaporated samples showed 
curdiness at 100° C. (212° F.) and 107.2° C. (225° F.) for 30 
minutes; 6.6 per cent at 112.8° C. (235° F.) for 30 minutes; and 
31.1 per cent at 121.1° C. (250° F.) for. 30 minutes. With raw 
milks coagulating with 75 per cent alcohol, 57.7 per cent showed 
curdiness at a temperature of 100° C. (212° F.) for 30 minutes, 80 
per cent at 107.2° C. (225° F.) for 30 minutes, 95.5 per cent at 112.8° 
C. (235° F.) for 30 minutes, and 100 per cent at 121.1° C. (250° F.) 
for 30 minutes. These figures show quite strikingly a difference in 



DETERMINING QUALITY OF MILK FOR CONDENSERIES. 



7 



condition of milk coagulating with 75 per cent alcohol, which renders 
it impossible to manufacture from it evaporated milk that will not 
give curdiness when using a sterilizing temperature necessary to in- 
sure a complete destruction of the bacteria. Samples of raw milk 
giving a coagulation with alcohol and showing curdiness when 
evaporated and sterilized can be sterilized without showing curdiness 



Raw milk not curdh'nq 
with 75% alcohol 



Raw milk curdling 
with 15% alcohol 




No curdiness 
PHHH Curdiness 

Fig. 2. — Extent of curdiness in evaporated milk sterilized at different temperatures. 

of the finished product in a mixture containing from 60 to 70 per 
cent of raw milks giving a negative alcohol test. This fact would 
account for the variation in heat taken by different batches from day 
to day. 

Undoubtedly there is received at every condensery some milk which 
will not stand the required heat when evaporated by itself, but 
which will go through all right when mixed with other milk. If the 



8 



BULLETIN 944, IT. S. DEPARTMENT OF AGRICULTURE. 



proportion of this milk is not too high no trouble will be experienced, 
but the proportion in some batches may be such as to cause consider- 
able trouble. 

It is interesting to know that raw milk with a low titratable 
acidity and which coagulates with alcohol and shows curdiness after 
evaporating and sterilizing can be made to stand sterilization with 
no resulting curdiness by mixing with it the proper amount of milk 
showing a high titratable acidity but no coagulation with alcohol. 

RELATIVE VALUE OF ACID AND ALCOHOL TESTS. 

The value of any practical test for determining the quality of milk 
for condensing must depend largely upon its ability to determine 
whether or not that milk, when evaporated to the required density, 
will withstand the necessary sterilizing temperature without becom- 



Alcohol Test 



SAMPLES* 
Aci'dity 12 II t o 9 8 7 6 5- 



SAMPLES— 

4 5 6 7 6 9 10 II 12 





No curd at 235°F. for JOmin. 
Curd at 235 " F. for 30 m In. 



Fig. 3. — The relation of titratable acidity and the alcohol test to coagulation of the 

evaporated milk. 

ing curdy. The flavor and odor are things which have to be deter- 
mined by the senses of taste and smell. The tendency of milk with 
objectionable flavor and odor to coagulate with alcohol indicates 
additional value of the test from this standpoint, especially where 
little attention is given to these factors. 

The preliminary work indicated clearly the unreliability of the 
acid test, as ordinarily used in the condensery, for determining the 
quality of milk for condensing. A comparison of the acid and 
alcohol tests in determining what milk when evaporated would 
stand sterilization without showing curdiness reveals the following: 

Of 90 samples of raw milk taken at the -weigh room and repre- 
senting a wide range of condition, 46 samples of the finished evapo- 
rated milk showed curdiness after sterilization and shaking. Forty- 
four of the evaporated-milk samples withstood sterilization, show- 
ing no curdiness after shaking. Analysis of Table 2 and figure 3 
shows that the alcohol test would have rejected 43 of the 46 samples 



DETERMINING QUALITY OF MILK FOR CONDENSERIES. 



9 



that showed curdiness after sterilization and shaking, while it would 
have rejected 2 out of 44 that were all right; that is, showed no 
curdiness. The acid test would have rejected 18 of the 46 samples 
showing curdiness after sterilization and shaking, while it would 
have rejected 21 of the 44 that showed no curdiness. 

The following tabulation shows the percentage of satisfactory and 
unsatisfactory milk samples that would have been retained or re- 
jected by the alcohol and acidity tests: 

Alcohol test. Acidity test. 
(Percent.) (Percent.) 

Satisfactory milk samples retained 95. 5 52. 3 

Satisfactory milk samples rejected 4. 5 47. 7 

Unsatisfactory milk samples retained 6. 5 60. 9 

Unsatisfactory milk samples rejected 93. 5 39. 1 

Table 2 gives a more concrete comparison of the relative value of 
the alcohol and acid tests in the work done at Grove City, Pa. 



Table 2. — Relative value of alcohol and acidity tests on samples run at Grove 

City, Pa. 







Alcohol test. 


Acidity test. 




Number 










Kind of samples. 


of sam- 










ples. 


Times 


Times 


Times 


Times 




correct. 


incorrect. 


correct. 


incorrect. 


Satisfactory 


44 


42 


2 


21 


23 


Unsatisfactory 


46 


43 


3 


18 


28 


Total 


90 


85 


5 ' 


39 


51 




100 


94.4 


5.6 


43.3 


56.7 



EXPERIMENTS AT CONDENSERIES. 

WORK AT FACTORY A. 

Realizing the importance of trying out the alcohol test under other, 
including commercial, conditions, the work was extended to a con- 
densery, which is designated as Factory A, 2 where considerable diffi- 
culty had been experienced in making an evaporated milk meeting 
the requirements of 26.15 per cent total solids and 8 per cent fat. 
The small laboratory apparatus used in the Grove City work was 
set lip in the laboratory of this plant and work of the same nature 
as that done at Grove City carried on. Samples of individual pat- 
rons' milk showing positive or negative reaction with alcohol were 
condensed to bring the product as nearly as possible to 18.15 per cent 
solids not fat, that being the portion of the evaporated milk causing 
the difficulty in sterilization. It was the aim to have the samples 
that were evaporated from raw milk showing no coagulation with 
alcohol slightly above the point of 18.15 per cent solids not fat, and 

2 The assistance of F. B. Evans in the work at this factory is acknowledged. 



10 



BULLETIN 944, U. S. DEPARTMENT OF AGRICULTURE. 



those from raw milk showing coagulation with alcohol slightly be- 
low this point. Samples not showing close to this schedule are not 
included in the discussion of results. 

The samples of evaporated milk put up in baby-size cans were run 
in a Berlin pilot sterilizer used by the plant in determining the 
amount of heat the different runs would stand. 

The results of this work did not agree closely with those obtained 
at Grove City. All the samples of raw milk showing coagulation 
with alcohol gave an evaporated milk that showed curdiness after 
sterilization at a temperature of 112.8° C. (235° F.) for 30 minutes. 
As the samples of raw milk, showing no coagulation with alcohol, 
gave evaporated milks that in the majority of cases also showed 
curdiness, no real comparison could be made as to the relative merit 
of the alcohol and acid tests. 

Table 3 shows the result of the work done at Factory A on indi- 
vidual patrons' milk samples. Of the 22 samples of raw milk show- 
ing no reaction with alcohol, 14, after evaporating, showed curdiness 
at the standard sterilizing temperature used, which happened to be 
about what was found necessary to insure a safe-keeping milk, while 
8 showed no curdiness. Of the 12 samples of raw milk showing 
coagulation with alcohol, all showed curdiness after they were evapo- 
rated and subjected to the standard sterilizing temperatures. 

Table 3. — Relation of alcohol test and titratable acidity in Factory A. Evapo- 
rated milk having close to 18.15 per cent solids not fat. Effect of sterilization 
noted after shaking for 1 minute. 





Raw milk not coagulating 
with 75 per cent alcohol. 


Raw milk coagulating 
with 75 per cent alcohol. 


Acidity. 


Total 


Effect of 
sterilization. 


Total 


Effect of 
sterilization. 




samples. 


Curdy. 


Not 
curdy. 


samples. 


Curdy. 


Not 
curdy. 


Per cent. 
0.11 to 0.12 








1 


1 




.12 to .13... 
.13 to .14... 
.14 to .15... 
.15 to .16... 
.16 to .17... 
.17 to .18... 
.18 to .19 


4 
3 
4 
3 
5 
3 


2 
2 
2 
3 
4 
1 


2 
1 
2 
0 
1 
2 


0 
3 
3 
4 
0 
1 
0 


0 
3 
3 
4 
0 
1 
0 


S 

0 
0 
0 
0 
0 
0 










Total 


22 


14 


S 


12 


12 


0 



The alcohol test was further tried out oh a commercial basis in 
this plant. The individual cans of milk received at the intake 
were tested with alcohol according to the method already described. 
All the milk showing no coagulation with alcohol was run in a sepa- 
rate vat and condensed in the large factory pan as a separate batch. 



DETERMINING QUALITY OF MILK FOR CONDENSERIES. 11 

A composite sample of the milks showing coagulation with alcohol, 
along with a sample of that showing no coagulation, was run in 
the laboratory apparatus as a means of comparison. Out of 4 trials 
the raw milk showing coagulation with alcohol gave an evaporated 
milk that in all 4 cases showed curdiness after sterilization at the 
standard temperature, while the evaporated milk from the raw 
milks showing no coagulation with alcohol showed curdiness in 3 
out of 4 cases. The 4 batches of milk, the individual cans of which 
showed no coagulation with alcohol and which were run in the 
large factory pan, all showed curdiness after sterilization. Several 
laboratory runs made on milk taken from the large receiving vat 
at different times, to get representative samples of the milk received, 
failed in all instances to give an evaporated milk that would meet 
the required standard and not show curdiness after sterilizing and 
shaking. 

The general failure of milk, accepted on the acid test at this con- 
densery, to withstand the necessary heat after being evaporated, 
suggested that it might be due to a deficiency in the composition 
and balance of milk salts, as reported by Sommer and Hart (2). 
The fact that the addition of a small amount of dibasic potassium 
phosphate, which is a normal constituent of milk, corrected the 
excessive tendency of the milk to curdle in sterilization indicates 
that this assumption was correct. 

Consideration of the manner in which milk at this plant was 
handled, in connection with the results obtained, indicates that the 
conditions were quite different from those that the average con- 
densery has to contend with, and for this reason it appeared highly 
desirable to try out the alcohol test at another place. 

WORK AT FACTORY B. 

The work was then continued in a condensery, designated Factory 
B, located in a region where dairying forms a minor part of the 
farm operations. As a result of this condition the milk received 
was not of good qualitj r . All the work done at this plant was on a 
commercial basis, the milk being graded at the intake and run into 
separate tanks according to its reaction with alcohol. Separate runs 
of the milk showing, respectively, coagulation and no coagulation 
with alcohol, were made in the factory pans, and after retaining the 
required amount of each batch of evaporated product for the experi- 
mental work, they were mixed in one tank and handled in the usual 
manner by the factory. Because of the small proportion of milk 
received that showed coagulation with alcohol, the batches from this 
kind of milk were smaller and in some cases it was necessary to hold 
them over until the next day in order to get enough for a run in the 



12 



BULLETIN 944, U. S. DEPARTMENT OF AGRICULTURE. 



factory pan. When this was found necessary the milk was cooled 
to a very low temperature and held in that condition overnight; 
only a very slight increase in acidity was shown. 

The evaporated milk from each run was standardized to show 
close to 18.15 per cent solids not fat. The samples from the raw 
milk showing no coagulation with alcohol were standardized to show 
slightly above this figure. All samples were sterilized in one of the 
large Fort Wayne sterilizers used regularly by the condense^. 

Four trials of grading and condensing milk on a commercial basis 
were made in this factory. The evaporated milk from the raw milks 
showing no coagulation with alcohol in all cases came through the 
sterilization process in fine shape, producing no curdiness and indi- 
cating that they would have stood more heat; in all four cases, also, 
the evaporated milk from raw milks showing coagulation with 
alcohol gave a pronounced curdiness that could not be removed by 
prolonged shaking. 

Table 4. — Results obtained by grading with the alcohol test at Factory B. 



Ravi 

Batch 
No. 


1 milk. 
Weight. 


Acidity. 


Reaction 
to alco- 
hol. 


Sclids 
not fat 
in evap- 
orated 
milk. 


Steriliza- 
tion o f 
evaporat- 
ed milk. 




Pounds. 


Per cent. 




Per cent. 




1 


12,400 


0.140 




17.96 


No curd. 


2 


4,250 


.170 




17.06 


Curdy. 


3 


10,100 


.150 




18. 53 


No curd. 


4 


9,100 


.175 


+ 


18. 16 


Curdy. 


5 


11,500 


.165 




18. 24 


No curd. 


6 


9,100 


.175 


+ 


18. 16 


Curdy. 


7 


12,400 


.145 




18.25 


No curd. 


8 


6.300 


.100 


+ 


17.91 


Curdy. 



Table 4 gives the data on the four trials of grading and condens- 
ing at this establishment. The titratable acidity of the lots of milk 
showing coagulation with alcohol is somewhat higher than that of the 
milk showing no coagulation with alcohol. We have no definite 
data that will enable us to say this difference in acidity would ac- 
count for the difference in coagulation. In order to throw some 
light on this question, four cans of the sterilized milk were sent to 
the laboratory where the hydrogen-ion concentration or true acidity 
was determined with the following results : 3 



Lot. pH. 

5 5.96 

6 5.80 

7 5.90 

8 5.84 



3 The determinations were made by H. F. Zoller, of the Dairy Division. 



DETERMINING QUALITY OF MILK FOR CONDENSERIES. 13 



While in each case the real acidity of the lot coagulating with 
alcohol and curdling in sterilization is higher, the difference is so 
small that it is very doubtful if it would more than counteract the 
effect of the higher solids of the corresponding lot. 

CONCLUSIONS. 

1. The acid test as ordinarily used will reject a portion of the un- 
satisfactory milks, but as a whole it is unreliable and inadequate as 
a means of determining the quality of milk for condenseries where 
evaporated milk is manufactured. 

2. There is no direct relation between the coagulation of milk 
with alcohol and its titratable acidity, but milks high in titratable 
acidity as a result of fermentation will in the large majority of cases 
show coagulation with alcohol. 

3. The alcohol test shows good possibilities as a practical and 
reliable test for determining the quality of milk for condenseries 
making evaporated milk. How generally the test can be applied will 
require further investigation at other condenseries. It is believed 
that it can be used to advantage in a large majority of average 
factories. 

LIST OF REFERENCES. 

(1) Rice, Frank E. 

1919. Milk with high apparent acidity. In Science, N. S., v. 50, no. 
1296, p. 424. 

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